Heater construction



Jan. 30, 1968 B, DMS ETAL 3,366,913

HEATER CONSTRUCTION Filed March l0, 1965 ff/a far?

United States Patent O 3,366,913 HEATER CNSTRUCTIN Bayard C. Davis,Lombard, Alvin Singer, Glencoe, and

Milford T. hapman, Jr., Addison, Ill., assignors, by

direct and mesme assignments, to Continental Sensing,

Inc., Melrose Parli, Ill., a corporation of Illinois Filed Mar. 10,1965, Ser. No. 438,488 11 Claims. (Cl. 33E-322) ABSTRACT GF THEDISCLOSURE A heater structure and a method for making it. A resistiveheating element is butt-welded to a pair of terminal segments. The weldjunctions 'are enclosed by tubular terminal elements which encompass theterminal segments and a portion of the heating element at each end. Theterminal elements are slightly chamfered to mate with peripheral groovesin the heating element, and are subjected to suitable swaging and/ ordrawing operations. The terminal elements and segments and the heatingelement are surrounded by a layer of heat conductive, electricallyinsulating material, and the entire structure is enclosed in a metallicsheath.

This invention relates to heater constructions and more particularly toan improved method of fabricating resistive heating elements.

It is an object of the present invention to provide an improved heaterconstruction.

Still another object of the present invention is to provide a heaterconstruction wherein the high resistance heating element employedtherein is bonded to the terminals of the heater by structurallyreinforced junctions.

An 'additional object of the present invention is to provide an improvedmethod of fabricating resistive heating elements so that the resultingheater construction is characterized by relatively long lived operation,an absence of hot spots and an ability to withstand normal handlingwithout having the continuity thereof disturbed.

Other objects and advantages of the present invention will becomeapparent from the following detailed description of one preferredembodiment thereof particularly when considered in conjunction with theaccompanying drawing wherein:

FIGURE 1 is a perspective View of a portion of a resistive heaterconstructed in accordance with the present invention; and

FIGURE 2 is an enlarged cross sectional view with portions broken awayto further illustrate the preferred fabrication technique of the presentinvention.

In general, the present invention is directed to an improved techniquefor fabricating heaters whereby the resistive heating element is joinedto low resistance terminals by structurally stable and reinforced weldedjunctions. As a result, the operational life of the heater isAincreased, the possibility of hot spot formations is minimized, and theheater can be normally handled without disturbing the continuitythereof.

Referring to the drawing, there is shown a preferred embodiment of aresistive heater fabricated in accordance with the method of the presentinvention. The particular embodiment illustrated is -a heater wherein aresistive heating element 11 and terminal conductors 12 and 13 that areassociated therewith are surrounded by a densely compacted, heatconductive insulating material 14 and confined within a suitableexternal sheathing 1S. However, it should be understood that thefabrication technique as hereinafter described in det-ail can be appliedto all forms of heaters whether or not such heaters employ theadditional protective sheathing (c g. stainless steel) and surroundingconductive insulating material (e.g. MgO).

Referring more particularly to FIGURE 2, the method of the presentinvention contemplates the joining of the resistive heating element 11to each of the terminal conductors 12 and 13 by means of reinforcedwelded junctions 12a and 13a respectively. In this connection, thefabrication of the heater 1t) is initiated by selecting a suitable highresistance material (e.g. Kanthal) having a preselected diameter andlength. This member serves as the heating element 11, and the dimensionsand thermal energy producing characteristics thereof are, in a wellknown manner, dictated by the particular application to which the heateris to be put.

After the selection of the appropriate heating element 11, a pair of lowresistance terminal segments 17 and 18 (eg. formed of nickel) areselected and joined to the oppositely disposed ends of the heatingelement. These segments constitute an integral portion of the terminalconductors 12 and 13. Preferably, the terminal segments 17 and 18 arebutt-welded to the ends of the heating element 11 and, accordingly,these segments preferably have cross-sectional dimensions correspondingto those of the heating element 11 to insure that these weldingoperations are effected in the most simple, reliable, and efficientmanner. After the welding of these segments has been completed, thereinforcement of the welded junctions is effected by the insertion ofthe partially fabricated heater into tubular terminal elements 19 and 20that form the remaining portion of the terminal conductors 12 and 13.The terminal segments 17 and 18 in certain applications (eg. when usingextremely long tubular terminal elements 19 and 20) will extend theentire length of these tubular terminal elements as depicted in FIG. l.In other constructions, the terminal segments 17 and 18 yare relativelyshort elements which do not extend along the entire length of theterminal elements.

The tubular elements 19 and 20 are formed with inside diameters thatcomplement the outside diameters of the joined terminal sections 17 and18 and heating element 11. The complementary dimensions of theseSubcomponents of the heater 10 are such that the joined terminalsections and heating element `are somewhat force fitted into the freeends of the tubular elements. In this connection, these components arejoined so that a major portion of the resistive heating element 11extends beyond and between the tubular elements 19 and 20 while at thesame time insuring that the welded junctions are fully encompassed bythe tubes.

To insure the proper positioning of the joined terminal sections andheating element and to facilitate the positive reinforced mounting ofthese joined elements, peripheral portions of the heating element 11adjacent the oppositely disposed ends thereof are formed with slightgrooves 11a and 11b. The partially joined assembly formed by the heatingelement 11 and terminal sections 17 and 18 is inserted into the tubularelements 19 and 2li to a point whereat the ends of the tubular elements,which are preferably slightly chamfered, are aligned with the grooves11a and 11b. To complete the assembly pursuant to the present invention,this fabricated structure is then subjected to suitable swaging and/ordrawing operations such that the free ends of the tubular elements 19and 2li are intimately formed about the welded junctions with theextreme chamfered ends thereof being forced into the grooves 11a and11b. This final forming of these overlapping sleeve type tubularelements 19 and 2t) is effected so that the possibility of any voidspots is eliminated.

t will be appreciated from the foregoing that the method of the presentinvention provides for the ready fabrication of structurally stableheater constructions. That is, any structural weakness in the heater asa result of the welding operations (eg. crystallization) is effectivelycompensated for by utilizing the overlapping sleeve type tubularelements 19 and 20 and forming (eg. by drawing and/or swaging) the endsof the elements into intimate overlapping and 4reinforcing contact withthe joined subassembly. Additional structural stability of the overallheater construction stems from forcing the slightly chamfered ends ofthe tubular elements into mating engagement with the peripheral groovesfia and lib. The fabrication method as described herein also results inthe elimi nation of any void spots adjacent the junction of the high andlow resistive components of the heater so that hot spot formations areprecluded.

When a heater constructed in accordance with the aforedescribed methodis designed to be confined within a densely compacted heat conductiveinsulating material and surrounded by suitable moisture imperviousmetallic sheathing as shown in the accompanying drawing, addi tionalfabrication steps are necessary to complete the entire assembly. In thisconnection, after the heater has been fabricated, a plurality ofsuitably apertured, structurally stable ceramic insulator strips (notshown) are strung onto the heater, including the terminal conductors,along substantially the entire length thereof. This partially assembledunit is then inserted into surgically clean metallic tubing. Thereafter,this assembled unit is subjected to suitable successive drawing and/ orswaging operations to insure that the insulator strips are denselycompacted about the heater and that the sheathing is drawn into intimatecontact with the materials confined therein. Upon completion of thisunit, suitable terminal elements (not shown) can be secured to the freeends of the terminal conductors thereby completing the confined assemblyfor operation.

lt will be appreciated from the foregoing that the present inventionprovides an improved technique for effecting tho fabrication of heatersindependent of the size or nature of the various components employedtherein. The method allows such heaters to be constructed in a reliableand efficient manner and calls for a minimum number of operational stepsabsent any critical drilling and/ or multiple welding operations.Obviously, various modifications of the fabrication technique of thepresent invention might be devised by one skilled in the art withoutdeparting from the invention, various features of which are set forth inthe accompanying claims.

What is claimed is:

ll. A method of fabricating resistive heaters which comprises joiningeach oppositely disposed end of a high resistance heating element to alow resistance terminal segment and thereby providing a heatersubassembly, inserting the joined terminal segments and heating elementinto the free ends of a pair of tubular terminal elements so that thefree ends of said terminal elements encompass the junctions of saidsubassembiy and so that a substantial portion of said heating elementextends between the free ends of said tubular terminal elements, anddrawing said tubular elements about the junctions of said terminalsegments with said heating element so that said junctions are positivelyconfined within the terminal elements and void spaces between the connedportions of said subassemblies and said confining portions of saidtubular terminal elements are eliminated.

Z. A method of fabricating resistive heaters which comprises weldingeach oppositely disposed end of a high resistance heating element havinga preselected cross sectional configuration and dimensions to a lowresistance terminal segment having a corresponding configuration anddimensions to thereby provide a heater subassembly, inserting the joinedterminal segments and heating element into the free ends of a pair oftubular terminal elements so that the free ends of said terminalelements encompass the welded junctions of said subassembly and so thata substantial portion of said heating element extends between the freeends of said tubular terminal elements, and drawing said tubularelements about the welded junctions of said terminal segments with saidheating element so that said junctions are positively confined withinthe terminal elements and void spaces between the confined portions ofsaid subassemblies and said confining portions of said tubular terminalelements are eliminated.

3. A method of fabricating resistive heating structures which compriseswelding each oppositely disposed end of an elongated high resistanceheating element to a low resistance terminal segment and therebyproviding a heater subassembly; inserting the joined terminal segmentsand heating element into the -free ends of a pair of tubular terminalelements so that the free ends of said terminal elements encompasses thejunctions of said subassembly and so that a substantial portion of saidheating element extends between the free ends of said tubular terminalelements; drawing said tubular elements about the welded junctions ofsaid terminal segments with said heating element so that said weldedjunctions are positively confined within the terminal elements and voidspaces between the confined portions of said subassemblies and saidconfining portions of said tubular terminal elements are eliminated; andenclosing said joined heating element, terminal segments and tubularterminal elements with a densely compacted layer of a heat conductiveinsulating material surrounded by a confining moisture impervioustubular metallic sheath.

4. A method of fabricating resistive heaters which comprises joiningeach oppositely disposed end of a high resistance heating element to alow resistance terminal segment and thereby providing a heatersubassembly; forming slight peripheral grooves in said heating elementadjacent each of said ends thereof and in preselected spaced relation tosaid junctions; inserting the joined terminal segments and heatingelements into a pair of tubular terminal elements having slightlycharnfered end portions so that the said tubular terminal elementsencompass the junctions of said subassembly in a sleevelikeconfiguration and so that a substantial portion of said heating elementextends between the slightly chamfered ends of said tubular terminalelements; and drawing said tubular elements about the junctions of saidterminal segments with said heating element so that said chamfered endportions are urged into mating relationship with said peripheralgrooves, said junctions are positively confined within the terminalelements and void spaces between the confined portions of saidsubassemblies and said confining portions of said tubular terminalelements are eliminated.

5. A method of fabricating resistive heaters which comprises weldingeach oppositely disposed end of a high resistance heating element havinga preselected cross sectional configuration and dimensions to a lowresistance terminal segment having a corresponding configuration anddimensions to thereby provide a heater subassembly; forming slightperipheral grooves in said heating element adjacent each of said endsthereof and in preselected spaced relation to said junctions; insertingthe joined terminal segments and heating element into the ends of a pairof tubular terminal elements having slightly chamfered end portions sothat the free ends of said terminal elements encompass the weldedjunctions of said subassembly and so that a substantial portion of saidheating element extends between the free ends of said tubular terminalelements; and drawing said tubular elements about the welded junctionsof said terminal segments with said heating element so that saidchamfered end portions are urged into mating relationship with saidperipheral grooves, said junctions are positively confined within theterminal elements and void spaces between the confined portions of saidsubasseinblies and said conining portions of said tubular terminalelements are eliminated.

6. A method of fabricating resistive heating structures which compriseswelding each oppositely disposed end of an elongated high resistanceheating element to a low resistance terminal segment and therebyproviding a heater subassembly; forming slight peripheral grooves insaid heating element adjacent each of said ends thereof and inpreselected spaced relation to said junctions; insetting the joinedterminal segments and heating element into the free ends of a pair oftubutar terminal elements having slightly chamfered end portions so thatthe free ends of said terminal elements encompass the junctions of saidsubassernbly and so that a substantial portion of said heating elementextends between the free ends of said tubular terminal elements; drawingsaid tubular elements about the welded junctions of said terminalsegments with said heating elements so that said chamfered end portionsare urged into mating relationship with said peripheral grooves, saidwelded junctions are positively confined within the terminal elementsand void spaces between the confined portions of said subassemblies andsaid conning portions of said tubular terminal elements are eliminated;and enclosing said joined heating element, terminal segments and tubularterminal elements with a densely compacted layer of a heat conductiveinsulating material surrounded by a confining moisture impervioustubular metallic sheath.

7. A terminal construction comprising a conductive element having aperipheral groove formed therein adjacent an end thereof; a terminalsegment having a crosssectional configuration corresponding to that ofsaid conductive element, said segment being electrically andmechanically connected to said end of said conductive element; and atubular terminal element having one end portion thereof slightlychamfered, said terminal element being drawn into direct forced contactwith and about a portion of said conductive element, the junctionbetween said conductive element and said terminal segment, and at leasta portion of said terminal segment so that said chamfered end portionmates with said peripheral groove.

8. A conductor structure comprising an elongated conductive element; apair of terminal segments each having a cross-sectional configurationcorresponding to that of said conductive element, one of said terminalsegments being Welded to each end of said conductive element to form ajunction therebetween; a pair of tubular terminal elements, one each ofsaid terminal elements being drawn into direct forced contact with andabout one of said terminal segments, said junction and a portion of saidconductive element; a densely compacted mass of heat conductiveinsulating material surrounding said conductive element, said terminalsegments and sai-d terminal elements; and a confining moistureimpervious tubular metallic sheath surrounding said mass of material.

9. A conductor structure as deued in claim 8, wherein said conductiveelement has a peripheral groove formed adjacent each of said junctions,and each of said terminal elements has a slightly chamfered end portion,said terminal elements being formed about said conduck tive element sothat said chamfered end portions mate with said grooves.

10. A heater structure comprising a high resistance heating elementhaving a peripheral groove formed therein adjacent at least one endthereof; a terminal segment having a cross-sectional configurationcorresponding to that of said heating element, said segment being joinedto said one end of said heating element; and a tubular terminal elementhaving one end portion thereof slightly chamfered, said terminal elementbeing drawn into direct forced contact with and about a portion of saidheating element, the junction between said heating element and saidterminal segment, and said terminal Segment, so that said chamfered endportion mates with said peripheral groove.

11. A heater structure as dened in claim 10, wherein said heatingelement, said terminal segment and said terminal element are surroundedby a densely compacted mass of heat conductive insulating material, andsaid mass of material is surrounded by a confining moisture impervioustubular metallic sheath.

References Cited UNITED STATES PATENTS 3,320,659 5/1967 Jerome 174-94 X3,138,656 6/1964 Merrell 174-90 FOREIGN PATENTS 60,105 10/1947Netherlands.

843,825 4/1939 France.

RICHARD M. WOOD, Primary Examiner. J. G. SMITH, Assistant Examiner.

